Re: Raw partitions vs. file system

S V <sv1_at_mindspring.com> wrote in article <01bce3d4$43dd9be0$db5c0c26_at_sfinance3>...

> I have got quite significant perfomance boost when I went FROM
> filesystem TO raw logical volumes on AIX 4.2 platform.
> And, in fact, Oracle perfomance tuning guide/tips for AIX platform
> does claim that Oracle performs significantly and consistently better
> when using raw devices than when using files.

This is interesting. We went thru a similar excercise more than a year ago and finally decide on using file systems (easier to administrate and move around for i/o load balancing) on a SMP box. At that time the docs for Oracle for that platform suggests not using raw devices due to the complexity of raw vs cooked files.

My initial reaction was to use raw devices, but after reading the docs and talking to local Oracle, the company decided to use cooked files instead. I was under the impression that there should be some noticeable increase in performance when using raw devices.

> Furthemore I found them to be easier to administer than filesystems.
> Just compare the time it takes to create 2G logical volume ( < 1 min)
> with a time it takes to create a filesystem the same size.

What about backups? To backup raw devices in Unix (when you don't have any special backup software) you need to use dd - and I won't rely on dd backups for a database. Also with file systems it's easy to move Oracle datafiles around between mount points to spread the i/o load - this is not possible with raw devices which makes fine-tuning of disk i/o performance a bit difficult. But then it also depends on the hardware. On another platform (MPP) we're using raw devices. If a disk controller/channel is suffering, you simply pull and swap physical disks (even between different nodes and even if the disk is part of a RAID set) to balance the i/o load. Not bad! :-)

> Besides,
> it's quite easy to delete by mistake an Oracle file on a filesystem
> (we have seen quite a few folks here begging for help after doing
> just that). Not so for raw logical volumes.

Sheez - this is dangerous. But then it means that too many people (and the wrong people) have root and oracle access to that box. Or that the file permissions of the datafiles are incorrect. Also a proper directory structure makes administration easier, especially if you're running multiple databases on the same box.

regards,
Billy Received on Wed Oct 29 1997 - 00:00:00 CST